The present invention relates to a light-transmitting object identifying apparatus and method which can easily authenticate a light-transmitting object.
Recent years have seen the remarkable widespread use of various types of vending machines targeted for a wide variety of merchandise. Some vending machines allow the use of bills, specific prepaid cards, and the like in addition to coins. Vending machines are installed in various places, and hence operate in various operation conditions. These machines are therefore required to exhibit satisfactory performance in every operation environment. This applies to mechanisms for authenticating coins, bills, and the like.
For example, the authenticity of a coin can be checked by examining its weight and shape, and hence a coin identifying mechanism can be mechanically formed.
In contrast to this, it is almost impossible to identify a bill with a mechanical device. For this reason, the degree of transmittance of a bill is optically discriminated. In a conventional bill discrimination method, a light source and a light-receiving element are spaced apart from each other by a predetermined distance, and a bill is conveyed between them to detect a light and dark pattern unique to the light source. The detected pattern is then compared with a reference light and dark pattern held in advance, thereby authenticating the bill.
In this method, however, since authentication is performed based on only light and dark patterns, even a copy of a negotiable instrument may be easily identified as a bill.
In order to solve this problem, a color sensor may be used. However, a color sensor is expensive and demands complicated signal processing, and hence cannot be used for a vending machine or the like which must meet a requirement for low cost as an absolute necessity.
In addition, a white light source (incandescent lamp) must be used as a light source. The white light source has a short service life, and burns out in a short period of time when the ambient temperature becomes high as in a case wherein the machine is installed on a road under the hot sun. In such a case, even if a bill is inserted into the vending machine, the bill is determined as a counterfeit and rejected.
In order to overcome this drawback, the color appearance of a bill may be determined by using, for example, two light-emitting diodes for emitting light beams having different wavelengths as light sources and receiving the light beams from the light-emitting diodes with one light-receiving element. Light-emitting diodes, however, vary in luminous efficacy. For this reason, the driving currents to the light-emitting diodes must be adjusted to equalize the performance ratios.
In addition, it is difficult to maintain uniform strength ratio for vending machines that can be installed outdoor because environmental conditions greatly vary. This equally applies to light-receiving elements. For this reason, reliable identification results cannot be obtained, and such vending machines are difficult to actually use.
In order to overcome such a drawback, a technique of using two light-emitting diodes, i.e., green and red light-emitting diodes, is disclosed in Japanese Patent Laid-Open No. 54-066894. In this technique, light beams emitted from the two light-emitting diodes are received by one light-receiving element, and the two light-emitting diodes are controlled to emit light beams in the same amount when there is no bill between the light-emitting diodes and the light-receiving element. When a bill comes between the light-emitting diodes the light-receiving element, an error signal is output in either of the two cases, i.e., a case wherein the output of the green light-emitting diode becomes equal to or higher than a reference level (the color of the bill is offset to green to some extent) and a case wherein the output of the red light-receiving element become equal to or higher than a reference level (the color of the bill is offset to red to some extent).
The technique disclosed in Japanese Patent Laid-Open No. 54-066894 is, however, based on the assumption that xe2x80x9cwhen the color of a bill does not shift (offset) to red or green, the amount of light received by the light-receiving element, i.e., the output, is at zero level as in the case of the absence of a billxe2x80x9d. In identifying such a bill, according to this technique, an error can only be determined when the color of the bill is offset to green or red to some extent. Some effect can be expected from this technique when a bill is printed in a specific color. If, however, bills are printed in full color as in Japan, it is almost impossible to authenticate bills by using the above technique.
If, for example, a bill is printed or copied in monochrome, no error can be determined. In practice, therefore, this technique cannot be used.
Furthermore, the service life of a light-emitting diode is inversely proportional to the emission time to a certain degree. If, therefore, the emission time of the light-emitting diode is too long, the diode deteriorates, resulting in a deterioration in identification performance. This is the problem that must be overcome by all means. That is, a deterioration in light-emitting diode needs to be suppressed.
The present invention has been made to solve the above problems, and has as its object to provide a light-transmitting object identifying apparatus which can automatically solve problems associated with variations in performance of each constituent members of a mechanism for detecting an identification object, changes in performance over time, and changes in performance due to environments with a simple arrangement, can be easily manufactured and adjusted, and has high reliability.
It is another object of the present invention to provide a light-transmitting object identifying apparatus which can express the difference in color taste between an authentic object and an identification target as a single signal with respect to the identification target, and can perform reliable authentication using a simple algorithm.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.